Roasting coffee transforms the chemical and physical properties of green coffee beans into roasted coffee products. The roasting process is what produces the characteristic flavor of coffee by causing the green coffee beans to change in taste. Unroasted beans contain similar if not higher levels of acids, protein, sugars and caffeine as those that have been roasted, but lack the taste of roasted coffee beans due to the Maillard and other chemical reactions that occur during roasting. The Maillard reaction is a chemical reaction between amino acids and reducing sugars that gives browned food its desirable flavor.
The vast majority of coffee is roasted commercially on a large scale, but small-scale commercial roasting has grown significantly with the trend toward “single-origin” coffees served at specialty shops. Some coffee drinkers even roast coffee at home as a hobby in order to both experiment with the flavor profile of the beans and ensure the freshest possible roast.
The coffee-roasting process follows coffee processing and precedes coffee brewing. It consists essentially of sorting, roasting, cooling, and packaging but can also include grinding in larger-scale roasting houses. In larger operations, bags of green coffee beans are hand- or machine-opened, dumped into a hopper, and screened to remove debris. The green beans are then weighed and transferred by belt or pneumatic conveyor to storage hoppers. From the storage hoppers, the green beans are conveyed to the roaster. Initially, the process is endothermic (absorbing heat), but at around 175° C. (347° F.) it becomes exothermic (giving off heat). For the roaster, because the beans are heating themselves, an adjustment of the roaster's heat source might be required. At the end of the roasting cycle, the roasted beans are dumped from the roasting chamber and air-cooled with a draft inducer.
In Vietnam coffee is often coated with oil (traditionally clarified butter) and a small amount of sugar prior to roasting to produce a “butter roast”. The roasting process results in an additional caramelized coating on the beans.
The most common roasting machines are of two basic types: drum and hot air. There are also packed-bed, tangential and centrifugal roasters. Roasters can operate in either batch or continuous modes. Drum roasting machines consist of horizontal rotating drums that tumble the green coffee beans in a heated environment. The heat source can be supplied by natural gas, liquefied petroleum gas (LPG), electricity or wood. The most common employ indirectly heated drums where the heat source is under the drum. Direct-fired roasters are roasters in which a flame contacts the beans inside the drum. Fluid Bed or hot air roasters force heated air through a screen or perforated plate under the coffee beans with sufficient force to lift the beans. Heat is transferred to the beans as they tumble and circulate within this fluidized bed.
Various attempts in the art have been made to roast coffee beans using microwave energy. For example, U.S. Pat. No. 4,326,114 discloses a microwave oven incorporated in a coffee bean roasting system and includes a rotatable microwave transparent tube or drum positioned within the same and at an angle to the horizontal, through which coffee beans are introduced at an upper end and flow in continuous agitation to the lower end while being subjected to microwave fields within the oven. At the lower end of the oven a separate section is preferably provided for subjecting the coffee beans to selective treatment during the final stages of the roasting process. In one form utilizing a unitary structure the separate section is provided by a conductive septum, which separates the oven into sections in which the power level is different. In the last section the power level is adjusted to control the final critical phase of the roasting process. The oven terminates into a cooling and quenching chamber from which the beans are delivered through a microwave trap to a further cooling stage to rapidly reduce their temperature to well below roasting.
Other devices have been disclosed for providing a device for roasting coffee beans in a conventional microwave oven. Such devices are disclosed in U.S. Pat. Nos. 7,235,764 and 6,436,457. PCT Application Pub. No. WO 2008/087622 A2 discloses an open roasting pan for inserting into a common or microwave based home oven for roasting coffee beans. The roasting, however, takes about 20 to 25 minutes.
A number of names have been commonly used to identify the various degrees of roast, such as City Roast and French Roast, based on the internal bean temperatures found during roasting. Often, a recipe known as a “roast profile” is followed to obtain certain flavor characteristics of the roasted coffee beans. A number of factors can affect the best profile to use, such as the coffee bean's origin, variety, processing method, moisture content, bean density and/or desired flavor characteristics. A roast profile can be presented as a graph showing time on one axis and temperature on the other, which can be recorded manually or using computer software and data loggers linked to temperature probes inside various parts of the roaster.
As the coffee beans absorb heat during roasting, the color shifts to yellow and then to increasingly darker shades of brown. During the later stages of roasting, oils appear on the surface of the bean. The roast will continue to darken until it is removed from the heat source. Coffee also darkens as it ages, making color alone a poor roast determinant. Most roasters use a combination of temperature, smell, color, and sound to monitor the roasting process. The most popular, but probably the least accurate, method of determining the degree of roast, however, is to judge the bean's color by eye. To obtain more accurate roasts, devices that quantitatively measure the roast have also been developed. For example, Agtron, Inc. of Reno, Nev. sells coffee roast analyzers that include spectrophotometers to analyze the degree of roast of ground and whole bean coffee. The Agtron analyzers use a narrow band of near-infrared energy to evaluate the coffee roast both as a whole bean and in a ground form.
Sound is a good indicator of temperature during roasting. There are two temperature thresholds called “cracks” that roasters listen for. At approximately 196° C. (385° F.), the coffee will emit a cracking or roasting sound. This point is referred to as “first crack,” marking the beginnings of a “light roast.” At first crack, a large amount of the coffee's moisture has been evaporated and the beans will increase in size. When the coffee reaches approximately 224° C. (435° F.), it emits a “second crack,” this sound represents the structure of the coffee starting to collapse. If the roast is allowed to progress too much further, the coffee will fully carbonize and eventually combust.
The following table sets forth various common roasts based on bean temperature and a description of the resulting roast at that temperature.
Green Beans - 22° C. (72° F.)Drying Phase - 165° C. (329° F.)Green coffee as it arrives at the dock.During the drying phase the beansThey can be stored for approximatelyare undergoing an endothermic12-18 months in a climate-controlledprocess until their moistureenvironment before quality loss iscontent is evaporated, signifyingnoticeable.first crack.Cinnamon Roast - 196° C. (385° F.)Light Roast - 205° C. (401° F.)A very light roast level that isModerate light brown, but stillimmediately at first crack. Sweetnessmottled in appearance. A preferredis underdeveloped, with prominentroast for some specialty roasterstoasted grain, grassy flavors, andhighlights origin characteristics assharp acidity prominent.well as complex acidity.American Roast - 210° C. (410° F.)City Roast - 219° C. (426° F.)Medium light brown, developedMedium brown, common for mostduring first crack. Acidity is slightlyspecialty coffee. Good for tastingmuted, but origin character is stillorigin character, although roastpreserved.character is noticeable.Full City Roast - 225° C. (437° F.)Vienna Roast - 230° C. (446° F.)Medium dark brown with occasionalModerate dark brown with lightoil sheen, roast character issurface oil, more bittersweet,prominent. At the beginning ofcaramel flavor, and acidity muted.second crack.In the middle of second crack. Anyorigin characteristics have becomeeclipsed by roast at this level.French Roast - 240° C. (464° F.)Italian Roast - 245° C. (473° F.)Dark brown, shiny with oil, burntNearly black and shiny, burnt tonesundertones, acidity diminished. Atbecome more distinct, aciditythe end of second crack. Roastnearly eliminated, thin body.character is dominant; none of theinherent aroma or flavors of thecoffee remain.
As noted in the table above, green coffee beans can be stored for approximately 12-18 months before quality loss is noticeable. However, for coffee beans to be considered part of the “current crop,” the storage time cannot exceed one year. If the green coffee remains in storage for longer than a year, it is considered old crop, and is less valuable because of its drier state. Once the coffee is roasted, however, the shelf life is significantly reduced.
After roasting, the coffee beans contain carbon dioxide that is emitted from the beans over time. For dark-roasted coffee, the beans can emit up to 10 liters per kilogram of coffee. The roasted coffee beans rapidly emit carbon dioxide over the first few days after roasting, then more gradually over the remainder of what is referred to as the degassing period. The carbon dioxide in the roasted coffee beans forms a barrier against oxidation, which is part of staling that degrades quality by altering the roasted coffee bean's essential oils and aromatic components. Exposure to moisture, high temperature and light after coffee beans have been roasted are also known to detrimentally affect the quality of the roasted coffee beans by accelerating oxidation of the roasted coffee beans and degrading their aroma. Thus, it is desirable to limit the time of storage of roasted coffee beans to obtain the best quality coffee.
As noted above, retention of carbon dioxide in the beans is desirable for a number of reasons. In addition, for preparing espresso, the carbon dioxide in the roasted coffee beans creates the highly desirable “crème” (the silky foam that forms on the top of the brewed coffee). Thus, it is desirable to utilize freshly roasted coffee beans that have retained significant amounts of carbon dioxide to produce the most desirable brewed coffee products.
Conventional coffee bean roasting methods, including those that have attempted to use microwave energy, have various disadvantages. One common disadvantage to all such roasting methods is that they take too much time to produce roasted coffee beans on demand. In addition, such roasting methods often require specialized equipment that is configured to prepare large quantities of roasted coffee beans, which may not remain fresh if not used within a few days. The methods used previously can also result in non-uniform heating of the roasted coffee beans, resulting in uneven or incomplete roasting of some of the beans.
Although standard multi-mode kitchen microwave devices have been used in the art for roasting coffee beans, the long processing times can result in burning of some of the coffee beans while other coffee beans in the same batch are under roasted. Non-uniform roasting will affect the taste and aroma characteristics of the resulting coffee brewed form such beans. As a result, the processing times, costs of production and losses in efficiency and quality of end product are compromised.
Improvements in the prior art methods have been subject to certain constraints. For example, the prior art specifically teaches that roasted coffee bean results are sensitive to the rate of rise of the temperature of the coffee beans during roasting. For roasting coffee beans in a roasting pan, the prior art teaches preheating a roasting pan to about 260° C. (500° F.), which is extremely hot and can result in sever burns if not handled correctly. At this temperature, the roasting takes about 8-10 minutes, with the first crack at approximately 5 minutes. After roasting, the beans must be quickly cooled to prevent further internal roasting as a result of heat that is retained in the beans from the roasting process.
Thus, there exists a need in the art to provide a method, system and device for improving coffee roasting. The various aspects and embodiments of the present invention, as described below, represent novel improvements on the above devices and methods of the prior art.